Electrical impedance tomography provides information of brain injury during total aortic arch replacement through its correlation with relative difference of neurological biomarkers

Postoperative neurological dysfunction (PND) is one of the most common complications after a total aortic arch replacement (TAAR). Electrical impedance tomography (EIT) monitoring of cerebral hypoxia injury during TAAR is a promising technique for preventing the occurrence of PND. This study aimed to explore the feasibility of electrical impedance tomography (EIT) for warning of potential brain injury during total aortic arch replacement (TAAR) through building the correlation between EIT extracted parameters and variation of neurological biomarkers in serum. Patients with Stanford type A aortic dissection and requiring TAAR who were admitted between December 2021 to March 2022 were included. A 16-electrode EIT system was adopted to monitor each patient’s cerebral impedance intraoperatively. Five parameters of EIT signals regarding to the hypothermic circulatory arrest (HCA) period were extracted. Meanwhile, concentration of four neurological biomarkers in serum were measured regarding to time before and right after surgery, 12 h, 24 h and 48 h after surgery. The correlation between EIT parameters and variation of serum biomarkers were analyzed. A total of 57 TAAR patients were recruited. The correlation between EIT parameters and variation of biomarkers were stronger for patients with postoperative neurological dysfunction (PND(+)) than those without postoperative neurological dysfunction (PND(−)) in general. Particularly, variation of S100B after surgery had significantly moderate correlation with two parameters regarding to the difference of impedance between left and right brain which were MRAIabs and TRAIabs (0.500 and 0.485 with p < 0.05, respectively). In addition, significantly strong correlations were seen between variation of S100B at 24 h and the difference of average resistivity value before and after HCA phase (ΔARVHCA), the slope of electrical impedance during HCA (kHCA) and MRAIabs (0.758, 0.758 and 0.743 with p < 0.05, respectively) for patients with abnormal S100B level before surgery. Strong correlations were seen between variation of TAU after surgery and ΔARVHCA, kHCA and the time integral of electrical impedance for half flow of perfusion (TARVHP) (0.770, 0.794 and 0.818 with p < 0.01, respectively) for patients with abnormal TAU level before surgery. Another two significantly moderate correlations were found between TRAIabs and variation of GFAP at 12 h and 24 h (0.521 and 0.521 with p < 0.05, respectively) for patients with a normal GFAP serum level before surgery. The correlations between EIT parameters and serum level of neurological biomarkers were significant in patients with PND, especially for MRAIabs and TRAIabs, indicating that EIT may become a powerful assistant for providing a real-time warning of brain injury during TAAR from physiological perspective and useful guidance for intensive care units.

The correlation coefficients among five parameters were higher in patients with PND than those in patients without PND (Table S1-S3).

0.071
The correlation coefficients among four biomarkers' area under curve in serum for five time points were significantly greater in patients with PND than those in patients without PND (Table S4-S6).Moreover, the concentrations of biomarkers in serum for each time point were showed in Table S7.Both the concentrations of TAU protein before surgery and right after surgery were significantly higher in PND (+) than those in PND (-) (Table S7).In addition, concentrations of GFAP 24h and 48h after surgery were significantly higher in PND (+) than those in PND (-) (600.05 (386.25 ~ 1654.76) vs. 411.82(327.52 ~ 503.07) and 716.71 (391.24~   1429.33) vs. 402.56(319.75 ~ 554.14), respectively) (Table S7).Unfortunately, after applying the multiple testing correction procedure, there was no significant difference between two groups (with α equal to 0.05).
In addition, the relative difference of neurological biomarkers in serum before and after surgery were obtained by calculation (Table S8).Results showed that only the variation between T2 and T1 for S100B protein was significantly different between PND (+) and PND (-) (0.57 (-0.33 ~ 3.3) vs. -0.11(-0.41 ~ 0.37), P=0.041) (Table S8).However, after applying the multiple testing correction procedure, there was no significant difference between two groups (with α equal to 0.05).
Table S4 Correlation coefficients of the area under curve (AUC) for concentration of each biomarker in serum for all patients.
**means p＜0.01.Data are presented as median (IQR) or mean±SD.RF: relative difference; T2T1: the relative difference between after and before surgery; T3T1: relative difference between 12h after and before surgery; T4T1: relative difference between 24h after and before surgery; T5T1: relative difference between 48h after and before surgery; * P value ＜ 0.05 means the value was significantly different between PND(+) and PND(-).
Table S9 Correlation coefficients between relative difference of serum biomarkers and EIT extracted parameters for patients with and without postoperative neurological dysfunction (PND).
*means p＜0.05.T2~T1: relative difference between after and before surgery; T3~T1: relative difference between 12h after and before surgery; T4~T1: relative difference between 24h after and before surgery; T5~T1: relative difference between 48h after and before surgery; HCA: hypothermic circulatory arrest; ΔARVHCA: the difference of average resistivity value before and after HCA phase; kHCA: the slope of electrical impedance during HCA phase; MRAIabs: maximum of the absolute value of resistivity asymmetric index; TARIabs: absolute value of time integral of resistivity asymmetric index; TARVHP: time integral of electrical impedance for half flow of perfusion.*means p＜0.05.T2~T1: relative difference between after and before surgery; T3~T1: relative difference between 12h after and before surgery; T4~T1: relative difference between 24h after and before surgery; T5~T1: relative difference between 48h after and before surgery; HCA: hypothermic circulatory arrest; ΔARVHCA: the difference of average resistivity value before and after HCA phase; kHCA: the slope of electrical impedance during HCA phase; MRAIabs: maximum of the absolute value of resistivity asymmetric index; TARIabs: absolute value of time integral of resistivity asymmetric index; TARVHP: time integral of electrical impedance for half flow of perfusion.**means p＜0.01.T2~T1: relative difference between after and before surgery; T3~T1: relative difference between 12h after and before surgery; T4~T1: relative difference between 24h after and before surgery; T5~T1: relative difference between 48h after and before surgery; HCA: hypothermic circulatory arrest; ΔARVHCA: the difference of average resistivity value before and after HCA phase; kHCA: the slope of electrical impedance during HCA phase; MRAIabs: maximum of the absolute value of resistivity asymmetric index; TARIabs: absolute value of time integral of resistivity asymmetric index; TARVHP: time integral of electrical impedance for half flow of perfusion.T2~T1: relative difference between after and before surgery; T3~T1: relative difference between 12h after and before surgery; T4~T1: relative difference between 24h after and before surgery; T5~T1: relative difference between 48h after and before surgery; HCA: hypothermic circulatory arrest; ΔARVHCA: the difference of average resistivity value before and after HCA phase; kHCA: the slope of electrical impedance during HCA phase; MRAIabs: maximum of the absolute value of resistivity asymmetric index; TARIabs: absolute value of time integral of resistivity asymmetric index; TARVHP: time integral of electrical impedance for half flow of perfusion.

Table S1
Correlation coefficients for EIT extracted parameters for all patients.**means p＜0.01

Table S2
Correlation coefficients for EIT extracted parameters for patients with PND.**means p＜0.01

Table S8
Relative difference of neurological biomarkers in serum before and after TAAR surgery for patients with and without postoperative neurological dysfunction (PND (+) and PND (-)).

Table S10 .
Correlation coefficients between relative difference of serum biomarkers and EIT extracted parameters for patients with normal and abnormal concentration of S100B before surgery.

Table S11 .
Correlation coefficients between relative difference of serum biomarkers and EIT extracted parameters for patients with normal and abnormal concentration of TAU before surgery.

Table S12 .
Correlation coefficients between relative difference of serum biomarkers and EIT extracted parameters for patients with normal and abnormal concentration of GFAP before surgery.HCA: hypothermic circulatory arrest; ΔARVHCA: the difference of average resistivity value before and after HCA phase; kHCA: the slope of electrical impedance during HCA phase; MRAIabs: maximum of the absolute value of resistivity asymmetric index; TARIabs: absolute value of time integral of resistivity asymmetric index; TARVHP: time integral of electrical impedance for half flow of perfusion.

Table S13 .
Correlation coefficients between relative difference of serum biomarkers and EIT extracted parameters for patients with normal and abnormal concentration of NSE before surgery.